The printing apparatus of a hand labeler generally has selector wheels supported on a shaft at one end portion of a printer frame and a type bearing member section at the other end portion of the frame. Endless printing bands made of a flexible material such as rubber or synthetic resin and formed on their outer surfaces with types and display characters are wound around the selector wheels and the type bearing member section. The selector wheels are rotated to rotate the endless printing bands to locate desired types on the outer surfaces of the type bearing member section where they can be printed, ink is applied to the types by an ink roller or the like, and the types can then be impressed on a label or the like.
Each endless printing belt is formed with types around one half its perimeter and display characters around the other half of its perimeter, the arrangement being defined so that the display character at the position viewable through a display window section provided in the printer frame corresponds to the type positioned at the type bearing member section.
Prescribed types can therefore be positioned at the type bearing member section by using a type select operating shaft to rotate the selector wheels while viewing the display characters through the display window section.
However, if an endless printing band is rotated beyond the prescribed rotation range when it is rotated by operating the type select operating shaft, the display characters may be rotated as far as the type bearing member section and be fouled by application of ink thereto by the ink roller. This leads to such problems as that the display characters become hard to see when selecting prescribed types while viewing the display characters through the display window section.
Various proposals have been made for preventing this fouling of the display characters (by ink application prevention means). In the "printing band structure" of Japanese Patent Publication No. Sho 62(1987)-33080, for example, a projection is provided on a rotating disk for rotating the endless printing band and a stop is provided in the vicinity of the rotation range region of the endless printing band. Owing to abutment of the projection on the stop, the rotating disk can rotate only within the prescribed region.
However, this device involves problems such as that the projection interferes with the display characters and that if the rotating disk is rotated with excessive force after the projection strikes on the stop, the endless printing band may elongate, causing it to print improperly or fall off.
Further, in the "printer" of Japanese Patent Application Laid-open No. Hei 6(1994)-155878, a protuberance is formed on the outer peripheral surface of the endless printing band to be engageable with a stop and the crest surface of a drive projection engaging with an indentation provided on the periphery of the selector wheel is formed as a slanted surface. When a selector wheel is forcibly rotated after the endless printing band has reached the limit position, the endless printing band slips.
In this printing apparatus, however, the problem arises that the slipping at the time the endless printing band is rotated with excessive force wears, cracks and otherwise damages the slanted surface of the endless printing band.
Moreover, since the outer peripheral surface of the endless printing band is formed with the protuberance, the problem arises that the number of type that can be provided on the endless printing band decreases.
Further, in the "device for preventing fouling of printer display characters" of Japanese Utility Model Application Laid-open No. 6(1994)-71146, the rotation range of the endless printing band is limited by abutment of a sectionally thick type portion formed on the outer perimeter of the endless printing band with a leg portion of an indicator.
Damage of the indicator and damage of the endless printing band by cracking and the like when excessive rotational force are also a problem in this device. Another problem is that the endless printing band may pass beneath the indicator.
In "printer" of Japanese Patent Publication No. Hei 4(1992)-34951, on the other hand, rotation of the endless printing band is limited by engagement between a tooth formed on the endless printing band and a stop shoulder.
This printing apparatus also has problems in that application of excessive rotational force elongates the endless printing band and causes wear, cracking and other damage.
Thus in all of these configurations the attempt to prevent fouling of the display characters by limiting rotation of the endless printing band to a prescribed region makes it difficult to avoid the direct or indirect action of large external forces on the endless printing band. They therefore encounter the problems of elongation and damage, the problem that the original purpose cannot be achieved because the projections ride over the stops, and other problems.
This invention was accomplished in the light of the aforesaid problems and has as an object to provide a printing apparatus which prevents fouling of the display characters on an endless printing band by keeping them from being positioned at the type bearing member section, i.e., from being brought opposite the ink roller.
Another object of the invention is to provide a prnting apparatus wherein the rotation of an endless printing band is limited in a manner that keeps excessive rotational force from acting on the endless printing band itself, thereby avoiding wear, cracking and other damage.
Another object of the invention is to provide a printing apparatus which minimizes the reduction in number of type caused by formation of a projection for limiting rotation of an endless printing band.
Another object of this invention is to provide a printing apparatus wherein forcible rotation of an endless printing band at its rotation limit causes idle rotation of the selector wheel and puts only moderate load on the endless printing band.
Another object of this invention is to provide a printing apparatus wherein the tension (degree of tautness) of an endless printing band can be regulated within a prescribed range.